Devices that convert digital In-phase (I) and Quadrature (Q) signals directly to In-phase/Quadrature (I/Q) modulated analog Radio-Frequency (RF) power are widespread in use today. Such devices have various names and abbreviations in literature, such as all-digital quadrature transmitter, Direct Digital to RF Modulator (DDRM), Digital to RF Converter (DRFC), Digital to RF Amplitude Converter (DRAC, RF-DAC). In this document the device is called an IQ to RF-power Digital to Analog Converter (IQ-RF-DAC).
A prior art IQ-RF-DAC performance has been achieved by switch-array topology. FIG. 1 shows an example of a switch-array IQ-RF-DAC 100, which is described by Chao Lu et al., see ref. [1]. The switch-array IQ-RF-DAC 100 of FIG. 1 is based on digitally modulating the conductance of switch arrays. Using logic AND gates, incoming digital Baseband (BB) bits control whether a Local Oscillator (LO) signal is reaching a unit switch gate or not.
For the IQ-RF-DAC 100 of FIG. 1, a radio-frequency output, RFout 101, is taken by combining the currents from first and second switch-array power amplifiers, I-PA 102 and Q-PA 103. A transformer 104 is used for combining the outputs of I-PA 102 and Q-PA 103 to RFOut 101. I-PA 102 and Q-PA 103 are identical and respond to In-phase (I) and Quadrature (Q) signals, respectively. Each one is split into multiple power cells 105, 106, discretely controlled by baseband signals. The baseband signal consists of thirteen bits, I-BB[12:0 ] 107 for the In-phase signal and Q-BB[12:0 ] 108 for the Quadrature signal, in a signed binary format. BB[12 ] indicates sign information and the rest of the bits are encoded with signal amplitude to enable the appropriate number of power cells. The sign bit I-BB[12 ] 109 is fed to a multiplexer 110, which further has as input an In-phase local oscillator signal, I-LO 111, and the sign bit 109 determines whether the positive I-LO signal, LO+ 112, or the inverted or opposite In-phase local oscillator signal, LO− 113, is used for switching switch gates of I-PA 102. The sign bit Q-BB[12 ] 116 is fed to a multiplexer 117, which further has as input a Quadrature local oscillator signal, Q-LO 118, and the sign bit 116 determines whether the positive Q-LO signal, LO+ 119, or the inverted or opposite Quadrature local oscillator signal, LO− 120, is used for switching switch gates of Q-PA 103. A unit power cell of I-PA and Q-PA 105, 106 is constructed with two AND gates 114, 115 and 121, 122, a switching pair 123, 124 and 125, 126 and its buffers 127, 128 and 129, 130. The enable signal bit, EN 131, 132 of I-BB[11:0 ] or Q-BB[11:0 ] is applied as one input of an AND gate 114, 115 and 121, 122, while the other input is connected with signed LO, LO+ 112, 119 or LO− 113, 120. The RF output, RFOut 101, conveys quantized baseband information, and thereby the IQ-RF-DAC 100 of FIG. 1 functions as a combination of digital-to-analog conversion, modulation and power amplification.